继承

1. 原型链继承，缺点：引用类型属性list改了，会影响其他实例

function Super() {
  this.list = [1,2]
}

Super.prototype.sayAge = function () {
  console.log(this.age)
}

function Sub(age) {
  this.age = age;
}

Sub.prototype = new Super()

var s1 = new Sub(30) 
s1.list.push(3)
var s2 = new Sub(30) 
s2.list // [1,2,3]

2. 借用构造函数，函数被call来使用，无法继承函数的原型

function Super() {
  this.list = [1,2]
}

Super.prototype.sayAge = function () {
  console.log(this.age)
}

function Sub(age) {
  this.age = age;
  Super.call(this)
} 

var s1 = new Sub(30)
s1.sayAge // undefined

3. 组合继承；结合上面的两个继承，互补利弊；唯一不足，实例通过Super.call有的属性，原型上 new Super()也有，重复了

function Super(name) {
  this.name = name
  this.list = [1,2]
}

Super.prototype.sayAge = function () {
  console.log(this.age)
}

function Sub(name, age) {
  Super.call(this, name)
  this.age = age;
} 

Sub.prototype = new Super()

var s1 = new Sub('kp', 30)

s1原型上，属性重复

4. 寄生组合式继承，Sub.prototype是一个空对象new F()【代替new Super()】这个空对象的构造函数原型是Super.prototype；解决上面问题： 原型上 new Super()也有，重复了 的问题

function object(o){ 
  function F(){} 
  F.prototype = o; 
  return new F(); 
} 

function Super(name) {
  this.name = name
  this.list = [1,2]
}

Super.prototype.sayAge = function () {
  console.log(this.age)
}

function Sub(name, age) {
  Super.call(this, name)
  this.age = age;
} 

Sub.prototype = object(Super.prototype)
// Sub.prototype = Object.create(Super.prototype) // 上一行代码，可以用Object.create，代替object这个自定义方法
Sub.prototype.constructor = Sub
var s1 = new Sub('kp', 30)
s1

s1原型上，没有重复属性

5. class 继承，采用的就是 【4. 寄生组合式继承】

class Super{
  constructor(name) {
    this.name = name
  }

  sayAge() {
    console.log(this.age)
  }
}

class Sub extends Super{
  constructor(name, age) {
    super(name)
    this.age = age
  }
}

var s1 = new Sub('kp', 30)

s1 - class继承